Lighting fixture



Dec. 21, 1943. c. J. ALLEN 2,337,437

LIGHTING FIXTURE Filed April 18. 1941 2/ lnven'bor:

Cart J. Atlen,

Patented Dec. 21, 1943 LIGHTDIG FIXTURE Carl J. Allen, Fort Benning, Ga., assignor to General Electric Company, a corporation of New York Application April 18, 1941, Serial No. 389,113

Claims.

My invention relates to lighting equipment of the type comprising an elongated light source of substantially uniform cross-sectionf'such as a tubular fluorescent lamp of the type now in extensive commercial use. More particularly my invention relates to lighting equipment of the above type for use in general illumination.

An object of my invention is to provide such lighting equipment which hields the eye of an observer from objectionably high brightness while producing a distribution of light flux of maximum angular spread, consistent with said shielding, in a plane transverse to the longitudinal axis of the lamp and of high intensity throughout its spread. Another object of the invention is to provide lighting equipment which controls the light emitted by the lamp to obtain a high utilization of the light flux for general illuminating purposes. Another object of the invention isto provide lighting equipment which emits light in opposite directions and controls the proportion of the total light flux emitted in each direction. Other objects and advantages of my invention will appear from the following description of embodiments thereof.

A feature of my invention is the use of a troughshaped reflector having an elliptical reflecting surface which is generated by a segment of an ellipse moved along a straight line. The segment is symmetrical with the major axis of the ellipse and the limits thereof are defined by the minor axis or by a chord normal to the major axis of the elipse. The elongated elliptical reflecting surface has a plurality of focal points, the locus of which is a straight line. For convenience this is called the focal line of the reflector. Of course, such a reflector has two focal lines, one included within the space defined thereby and the other outside said space. It will be understood, however, that the first of these is intended where reference is made to the focal line hereinafter.

An elongated, tubular fluorescent lamp, which is a diifuse, linear lightscurce, is mounted with its longitudinal axis parallel to the focal line of the reflector and in the plane generated by the major axis of the ellipse as the segment thereof is moved to generate the reflecting surface. When the surface of the reflector is specular it reflects an image of the lamp. This image, as well as the lamp itself, is of such brightness that it is desirable to shield the image and the lamp from the eye of an observer. I have discovered and demonstrated that the reflector hields both the lamp and the reflected image thereof from transverse view from any point above a plane making a predetermined angle with a horizontal plane when the lamp is tangent to said first mentioned plane and when said plane include an.

edge of the reflector and intersects the elliptical reflecting surface at a line whereat a plane tangent to said surface is normal to said first mentioned plane. I .have also discovered and demonstrated that when the lamp is so positioned in the reflector, the lighting equipment provides a distribution of light flux of maximum transverse spread and of high gradient of candlepower near the outer edge thereof. Such a distribution gives a highly desirable uniformity of illumination on a plane interrupting such flux and parallel to the plane generated by the minor axis of the ellipse generating the reflector to permit wider spacing of the units of the lighting equipment for a given ratio of maximum to minimum illumination on said plane. Further, such a distribution gives an eminently satisfactory relation between illumination on planes normal and parallel to the plane of said minor axis.

In the accompanying drawing 1 have illustrated a species of my invention in which:

Fig. 1 is a perspective view of a multi-lamp unit comprisingmy invention; Fig. 2 is a transverse sectional view along the line 2-.2 of Fig. 1: Fig. 3 is a transverse sectional view along the line 3-3 of Fig. 2; and Fig. 4 is a diagrammatic cross-sectional view of a single lamp and a reflector therefor.

Referring to Figs. 1 to 3 of the drawing, the

lighting unit according to the invention comprises a frame consisting of a pair of end plates or members In and H fastened to and supported by the elongated, hollow member l2. Said member I2 is provided with a pair of spaced rods l3 (only one of which is shown) for suspending the unit from the ceiling of .the interior to be illuminated and accommodates the transformer for the lamps l6. Said lamps l6 are mounted in spaced parallel positions between the end plates l0 and II and are removably secured thereto by the sockets l1 fastened to said end plates I0 and Il. Sockets H are of the type described in the U. S. Reissue Patent No. 21,545, issued August 2'7,

1940, and assigned to the assignee of the present application. The lamps l6 are of the type disclosed in the U. S. Patent 2,182,732, issued December 5, 1939, and assigned to the assignee of the present application. A plurality of transverse louvers I! are bolted to the channel member I! in equally spaced parallel positions along the lamps IS. The width and the spacing of the louvers l8 determine the angle at which the lamps it are shielded from longitudinal observation. This is called the longitudinal shielding angle and is measured from a horizontal plane to a plane including the bottom edge of a louver iii to the lowest part of the U-shaped slot I! in the adjacent louver. A longitudinal shielding angle of about 28 degrees is preferred.

The U-shaped slots IS in the louvers l8 accommodate the lamps I6. Said louvers l8 also have elliptically shaped slots "to accommodate and support the elliptical reflector members 2|, which extend through each of said louvers 8, in spaced, parallel, opposing positions to the lamps l6, as shown. The space between the top edges of the reflectors 2| is slightly wider than the diameter of the lamps l6 and permits replacing of the lamps |B from above without disturbing the other elements of the unit.

Fig. 4 of the drawing is a diagrammatic, transverse cross-sectional representation of lamp and reflector of the unit shown in Figs. 1 to 3. The ellipse used in the generation of the elongated reflectors 2| of the unit has a major axis of approximately 9.7 inches and a minor axis of approximately 5% inches. The outside diameter of the lamp I6 is 1 inches. The surfaces of the reflectors 2| are specularly reflecting and are capable of reflecting a virtual image of the lamp. Polished aluminum surfaces are preferred, though mirrors constituted of light transmitting glass or plastic backed with metal may be used. The longitudinal axis of the lamp I6 lies in the plane generated by the major axis of the ellipse as the ellipse is moved along a straight line to generate the reflecting surfaces 2|. When the lamp and the reflected image thereof is to be shielded from observation from points above a plane making a dihedral angle of less than 90 degrees with a horizontal plane, said first mentioned plane must intersect one of the reflectors 2| at the line of tangency of a plane C drawn tangent to said reflector 2| and must be normal to said last-mentioned plane. Further, the lamp must be mounted in such position thatthe plane intersecting the reflector 2| is tangent to the lower arcuate portion thereof and the lower edge of the opposite reflector 2| must lie in said plane. I prefer to shield the lamp and its image from transverse observation from points above a plane A making a dihedral angle of degrees with a horizontal plane B. I call this angle the transverse shielding angle. As shown in Fig. 4 of the drawing, the lower edge of the reflectors 2| then terminate short of the minor axis of the ellipse and the longitudinal axis of the lamp in this example is offset from one focal line in the direction of the conjugate focal line. Obviously, the said longitudinal axis of the lamp will occupy different positions with respect to the focal line of the reflector 2| when lamps of larger or smaller diameter than that given in the example are used, or when the shielding angle is changed.

In the embodiment of the invention illustrated in Figs. 1 to 4, the space between the top edges of the reflectors 2| is an unobstructed passage or aperture for the light emitted upward by the lamp l6 and the separation of said edges is such that lines drawn from the longitudinal axis of the lamp to each of said edges diverge at an angle of 94 degrees. Approximately one-third of the total light output of the unit is then emitted upwardly for illuminating the ceiling and about two-thirds thereof downward. The total light output of the unit is approximately 81 per cent of the total light output of the lamps i6.

The ratio between the upwardly passing component oi emitted light and the downwardly emitted component thereof is controlled by the relative size of the opening between the top edges and the'bottom edges of the reflectors 2|.

The downward distribution of light from the unit described above is highly advantageous for the illumination of extended areas since the peak candle power is at an angle of between 25 and 30 degrees from the plane generated by the major axis of the ellipse and the candle power at an angle of 45 degrees from said plane is 27 per cent of the peak candle power. The distribution of the light is measured in a plane intersecting the plane generated by said major axis and parallel to said minor axis. Thus the unit provides a downwardly-directed, wide-spread light flux having a high gradient of candle power at the outer portions thereof. Such lighting units may be spaced apart at least one and one-half times the height of the unit above the horizontal surface to be illuminated without causing areas of objectionably low levels of illumination on said surface and between said units.

While I have shown and described a particular embodiment of my invention, it will be understood that I contemplate that the transverse and lateral shielding angles of the unit may be changed to suit the desires of the user, that lamps of greater or lesser diameter than one and one-half inches may be used and that the length of either the major or minor axis, or both, of the generating ellipse may be changed without departing from the invention. For example, a unit having a transverse shielding angle of 50 degrees, a reflecting surface generated by an ellipse having a major axis of 8 inches and a minor axis of 5 inches and a lamp having a diameter of 1 inch is within the scope and gives the advantages of the invention when the lamp is mounted in the reflector in such position that the lower arc thereof is tangent to a plane which makes a dihedral angle of 50 degrees with a horizontal plane, intersects the "surface of the reflector at the line of intersection of a plane drawn tangent to said surface and which is perpendicular to said last named plane. In such a unit the plane tangent to the lamp intersects the minor axis inside the ellipse and I then prefer to make the lower part of the reflector extending from said minor axis to the plane tangent to the lamp planar in shape to secure the desired shielding angle for the lamp and the reflected image thereof, though it will be understood that this part of the reflector may have an elliptical shape when desired.

While the lighting units described above are effective for shielding the lamps and the reflected images thereof from view above the plane tangent to the lamp in the usual installation where the lamps do not extend above the top edges of the reflector and the units are not viewed from above. I contemplate that the lamps may extend above the top edges of the reflectors 2| and thus be visible from points of observation above or below the unit when lamps of comparatively large diameter with respect to the size of the reflector are used and that the lamps may be visible through the top of the unit from escalators or balconies above the hangin-gheight of the unit. In such unusual instances the lamps may be concealed by interposing light diffusing or opaque elements, such as metal or plastic strips, between the lamps and such points of observation. Said such strips may be contiguous with or constitute extensions of the upper edges of the reflectors 2| and are in parallel, vertical planes having the same separation as said upper edges. Further, when the 11: wardly emitted light of the lamps I6 is not desired for illumination of the ceiling, elliptical reflectors having no opening above the lamps.

radiation to obtain high utilization thereof.-

Further, such units are useful in conjunction with sleeves which surround, orpartially surround, the lamps and which are light diffusing or which emit diffused light under irradiation by said lamps. Such sleeves are mounted. in the same position in the reflector .as the lamps IS in the above units,

While I have mentioned heretofore various advantages of the fixture described and illustrated, another advantage thereof is a low rate of depreciation of light output due to the fact that dust can collect only on the top of the lamps [6 since these are the only surfaces which are not either vertical or facing downward. When the reflecting surface is partially specular so that the image is partially diffused, the reflectors 2| shield the brightest part of the image from transverse tical reflector with its longitudinal axis lying in the major axis of the elliptical reflector and parallel to but offset from the loci of the foci of said reflector whereby said lamp and the reflected image thereof are shielded from observation at angles greater than the dihedral angles made by said normal planes with said common plane and the light flux is of maximum transverse spread, consistent with such shielding, and of high gradient of candlepower at the outer portions thereof.

2. A lighting unit comprising an elongated, tubular lamp and an elongated, trough-shaped reflector elliptical in cross-section, presenting an image reflecting surface to said lamp and having an opening saidreflector being symmetrical with the major axis of the ellipse, the edges of said reflector defining said opening .being'in a common plane perpendicular to and intersecting said major axis between the focal points of said ellipse, said edges also being disposed in planes which are normal to the image reflecting surface of said reflector and which intersect inside said reflector,

' the dimensions of said reflector being such that observation. When desired, the sides of the fixture illustrated in Figs. 1 to 3 consist of light diffusing, light colored elliptically shaped strips of plastic material, such as Textolite instead of a metal reflector 2|. This material transmits most of the light from the adjacent lamp l6 and the strips appear as elongated luminous elements of comparatively low surface brightness to give an aspect of inappreciable weight to the fixture.

The louvers l8 consist of metal, such as aluminum, though louvers of light diffusing plastic material may be used. Lighting units embodying the invention are suspended with the plane generated by the major axis of the generating ellipse normal to the surface to be illuminated. Usually this surface is in a horizontal plane, through it may be in any plane from a horizontal to a vertical one.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A lighting unit comprising an elongated, tubular lamp and an elongated,trough-shaped reflector elliptical in cross-section, presenting an image reflecting surface to said lamp and having an opening for the passage of light from said unit, said reflector being symmetrical with the major axis of the ellipse, the edges of said reflecsaid normal planes make an acute dihedral angle of the order 40 to 50 degrees with the common plane of said edges, said lamp being disposed tangent to each of said normal planes and in the space between said normal planes and the vertex of said ellipticalreflector with its longitudinal axis lying in the major axis of the elliptical reflector and parallel to but offset from the loci of the foci of said reflector whereby said lamp and the reflected image thereof are shielded from observation at angles greater than the dihedral angles made by said normal planes with said common plane and the light flux is of maximum transverse spread, consistent with such shielding, and of high gradient of candlepower at the outer portions thereof.

3. A lighting unit comprising an elongated, tubular lamp and an. elongated, trough-shaped reflector elliptical in cross-section, presenting an image reflecting surface to said lamp and having opposed, elongated openings of different widths for the passage of light in opposite directions from said unit, said reflector being symmetrical with the major axis of the ellipse, the edges ofsaid reflector defining the opening of larger width being in a common plane perpendicular to and intersecting said major axis between the focal points of said ellipse, said edges also being disposed in planes which are normal to the image reflecting surface of said reflector and which intersect inside said reflector, the dimensions of said reflector being fsuch that said normal planes make an acute dihedral angle with the common plane of said edges, said lamp being disposed tangent to each of said normal planes and in the space between said normal planes and the vertex of said elliptical reflector with its longitudinal axis lying in the major axis of the elliptical reflector and parallel to but offset from the loci of the foci of said reflector whereby said lamp and the reflected image thereof are shielded from observation at angles greater than the dihedral angles made by saidnormal planes with said common plane and the light flux is of maxi mum transverse spread, consistent with such shielding, and of high gradient of candlepower at the outer portions thereof.

4. A lighting unit comprising an elongated, tubular lamp and an. elongated, trough-shaped reflector elliptical in cross-section, presenting an image reflecting surface to said lamp and having for the passage of light from said unit,

opposed, elongated openings or diiierent widths for the passage or light in opposite directions from said unit, both 01 said openings being larger in width than the diameter ot'said lamp, said reflector being symmetrical with the major axis of the ellipse, the edges of said reflector defining the opening or larger width being in a common plane perpendicular to and intersecting said major axis between the focal said edges also being disposed in planes which are normal to the image reflecting surface of said reflector and which intersect inside said reflector, the dimensions of said reflector being such that said normal planes make an'acute dihedral angle with the common plane of said edges, said lamp being disposed tangent to each of said normal planes and in the space between said normal planes and the vertex 01' said elliptical reflector with its longitudinal axis lying in the major axis of the elliptical reflector and parallel to but offset from the loci of the loci of said reflector whereby said lamp and the reflected image thereof are shielded from observation at angles greater than the dihedral angles made by said normal planes with said common plane and the light flux is oi. maximum transverse spread, consistent with-such shielding, and of high gradient of candlepower at the outer portions thereof.

5. A lighting unit comprising an elongated, tubular lamp and an elongated, trough-shaped reflector elliptical in cross-section, presenting an points of said ellipse,

assmsv image reflecting surface to said lamp and having opposed, elongated openings or diflerent widths for the passage or light in opposite directions from said unit, said reflector being symmetrical with the major axis or the ellipse and having also a plurality of spaced, transversely extending louver-s disposed between said lamp and the opening of larger width, the edges 01 said reflector defining the opening of larger width being in a common plane perpendicular to and intersecting said major axis between the focal points of said ellipse, said edges also being disposed in planes which are normal to the image reflecting surface 01' said reflector and which intersect inside said reflector, the dimensions of said reflector being such that said normal planes make an acute dihedral angle with the common plane or said edges, said lamp being disposed tangent to each of said normal planes and in the space between said normal planes and the vertex of said elliptical reflector with its longitudinal axis lying in the major axis of, the elliptical reflector and parallel to but offset from the loci of the foci of said reflector whereby said lamp and the reflected image thereof are shielded from observation at angles greater than the dihedral angles made by said normal planes with said common plane and the light flux is of maximum transverse spread, consistent with such shielding, and 01' high gradient of candlepower at the outer portions thereof.

CARL J. ALLEN. 

